1. Field of the Invention
The present invention relates to an aqueous solution of an extract obtained from ginkgo leaf (hereinafter referred to "ginkgo leaf extract") using a hydrous organic solvent.
2. Related Art Statement
Conventionally, in order to improve the circulation of blood throughout the brain, those medicines containing the ginkgo extract as an effective ingredient have widely been used in France or Germany. It is well known that the ginkgo extract provides useful pharmacological action of relaxing muscle of the blood vessel contracted by effect of stress and mental tension to reduce resistivity of peripheral artery and pharmacological actions of expanding the blood vessels, and accelerating the speed of blood circulation so that the volume of blood can eventually be increased. It is also known that the ginkgo extract effectively deals with peripheral blood vessel disease without causing side effect. By virtue of those advantageous reasons, the ginkgo extract is not only used for composing medicines, but also partly available in markets as health-promoting food. It is expected that ginkgo extract based drugs and foods will further come into wider use in the market.
On the other hand, the above ginkgo leaf extract is found still defective in that it is hardly soluble in water in spite of its solubility, for example, in organic solvent like alcohol. As a result, in order to allow consumers to internally take the ginkgo leaf extract without using alcohol, pharmacists are obliged to charge pulverized extract in solid capsules or mold it into tablets, thus limiting the application of this product to the preparation of solid medicines. However, those aged people and the sick find it easier to take liquid product than a solid one. Furthermore, liquid product can be more effectively absorbed into human body than the solid one, and thus, there is a growing demand among those concerned for an alcohol-free liquid product composed of the ginkgo leaf extract.
The present inventors have previously proposed a cooling beverage (soft drink) in which a ginkgo leaf extract is dissolved in water by using polydextrose (Japanese Patent Application No. 63-295372) as a means for solving the above problem.
However, since the above cooling beverage containing a ginkgo leaf extract is provided in the form of the ginkgo leaf extract previously diluted with water, a concentration of the ginkgo leaf extract necessarily becomes a dilute aqueous solution of 0.04 to 0.2% considering an appropriate intake amount of ginkgo leaf extract for adult (about 120 mg) and the appropriate diluted amount as a cooling beverage. Thus, there are inconveniences that many containers must be used and disposed, and purchase or storage is cumbersome for habitual use in a family.
In order to solve these inconveniences, a method employed is that a solution containing a high concentration of the ginkgo leaf extract is prepared and diluted with water when taking it. In fact, the ginkgo leaf extract has been sold in France or Germany in the form of a highly concentrated solution. However, this highly concentrated solution uses a high content of ethanol (to the extent of 30 to 50%) in order to dissolve the ginkgo leaf extract so that it is inappropriate for selling the solution to the general public as a health food. Also, in Japan, the ethanol content in non-alcoholic drinks is limited to 1% or less, so that such a high ethanol content solution cannot be marketed as non-alcoholic drinks.
On the other hand, there has been proposed a method in which the ginkgo leaf extract is dissolved in water with high concentration by using a sugar alcohol as a method of preparing high concentration solution of the ginkgo leaf extract without using an organic solvent such as ethanol. However, the present inventors have already pointed out (see Japanese Patent Application No. 63-295372) that when the method is applied to the above preparation of the ginkgo leaf extract cooling beverage, it becomes unsuitable for drink since an amount of the sugar alcohol becomes too excessive. When it is made in a high concentration solution, it is diluted with water when taking it so that there occurs no problem which is caused by excessive amount of the sugar alcohol.
However, according to the investigation by the present inventors, it was found that when a high concentration aqueous solution of the ginkgo leaf extract is to be prepared by using a sugar alcohol which is obtained by reduction of a monosaccharide (hereinafter referred to "monosaccharide alcohol") such as sorbitol, stable high concentration aqueous solution can not be obtained due to small stabilizing action of the monosaccharide alcohol. To the contrary, when a large amount of monosaccharide alcohols is added in order to obtain a stable high concentration aqueous solution, the monosaccharide alcohol is precipitated as crystals. Also, when a sugar alcohol obtained by reduction of oligosaccharide having a large molecular weight is used, it became clear that a high concentration aqueous solution which can be practically used can not be obtained since viscosity or transparency of the aqueous solution is lowered.